Method for controlling rolling movements of a ship



June 30, 1959 F. LJUNGSTRUM METHOD FOR CONTROLLING ROLLING MOVEMENTS OFA SHIP Filed Feb. 17, 1954 3 Sheets-Sheet 1 June 30, 1959 F. LJUNGSTRGMMETHOD FOR CONTROLL ING ROLLING MOVEMENTS OF A SHIP Filed Feb. 17, 19543 Sheets-Sheet 2 June 30, 1959 F. 'LJUNGSTRGM 2,892,435

I METHOD FOR CONTROLLING ROLLING MOVEMENTS OF A SHIP Filed Feb. 17, 19543 Sheets-Sheet 3 Fig."

United States Patent METHOD FOR CONTROLLING ROLLING MOVEMENTS OF A SHIPMy invention relates to ships and more particularly to anti-rollingmeans for such ships.

In spite of the extraordinary development of shipping experienced withthe introduction of engine-operated ships, nevertheless the varioustypes of ships hitherto brought into use have all been marked by acommon weakness or imperfection consisting in their tendency to rollthrough continuously repeated angular movements abouta longitudinalaxis.

Even ultra modern ships now built, show qualities inferior" to those ofearlier constructions with respect to their increased tendency to roll.

Many propositions have been tried with a view to reducing the rolling ofships. According to one proposition, the ship is provided with watertanks, generally placed at the bottom of the ship on both sides of thefore and aft center line thereof, said tanks having for their objecttobe alternately filled and emptied in order to move the center of gravityof the ship in a lateral di-' rectionthereby counteracting the rollingof the ship. This way does not lead to any favourable result.

It is also known to adjust the metacentric height of the ship by meansof water tanks or stowing of the cargo One main object of my inventionis to provide anti-' rolling means in ships adapted to maintainrollingmovements at a minimum particularly when sailing through a turbulentsea.

Further objects and advantages of my invention will be'apparent from thefollowing description considered in connection with the accompanyingdrawings, which form part-of this specification and of which:

Fig. 1 is a side elevational view of a ship constructed according to myinvention.

nice

Fig. 8 is a cross section of the hull of a ship embodying a modificationof my invention.

Fig. 9 is a cross section of the hull of a ship of the conventionaltype.

Figs. 10 to 12present curve diagrams.

The hull of the ship illustrated in the Pigs. l-4 isshown in the Britishpatent to Ljungstrom No. 521,734. In cross section, the hullsubstantially has the form of a V, the legs 10 of which constitutecircular arcs with the radius (p. The ship may be built with ribs orframes,

all of which have the same radius of curvature. In its' longitudinaldirection the hull has the form of a partial body of revolution, thecenter of which is located amidships above the ship, as is indicated bythe radius R.

When a ship of this and analogous types swings about its longitudinalaxis so as to cause its longitudinal vertical plane 12 passing throughthe center line of the ship to take an inclined position as is indicatedin Fig. 3, the area of a surface defined by the longitudinal verticalplane 12 and the hull at the water-line 14 will increase, calculatedfrom said longitudinal vertical plane 12 in the direction of theswinging motion, the area of such surface on the opposite side of saidplane being reduced correspondingly at the same time. The same eifect isattained with a hull forrn made according to Fig. 8, the

, side portions 16 of which converge in a downward direction. A Theseside portions need only have an extension in the vertical directioncorresponding to the angles of list to be calculated with so as toensure the water-line substantially to be located adjacent saidportions. The

chain-dotted line 18 indicates the position of the waterline at acertainlist of the ship. In this case, too, the area of the above definedsurface at the water-line has been increased in the listing direction,as seen from the longitudinal plane 12 relative to the opposite side. In

the conventional hull of a ship with parallel sides 20, i

on the other hand, the proportion between the two areas above definedwill not be changed, as will easily be understood from Fig. 9. Again, ifthe loading of the ship is reduced, its breadthin the water-linedecreases when constructed according to my invention, but will remainunchanged when constructed with the form shown in Fig. 9. The advantagesattained with the form of the hull according to my invention will becomestill more evident by the following explanation.

The forepart 22 of the hull has, in addition to the ob- 'tuseintersectional angle of the sides 10 of the hull at the keel, a depth orcross-sectional area below the water-line decreasing continuously towardthe bow. This form of the forepart, which in the illustrated embodimentis curved upwardly, may begin from approximately amidships. Theafterpart of the hull may have substantially Fig. 2 is a cross sectionof the hull proper of the ship taken on the line II-Il of Fig. l.

1 Fig. 3 shows the hull of the ship in the same section a in Fig. 2 butin an inclined position relative to the surface of the water, a sectionon the lines III-III of Fig. 1 also being indicated with chain-dottedlines in this figure.

Fig. 4 is a cross section through the hull' of the ship corresponding toFig. 2 but on a larger scale.

Fig.5 shows a detail of Fig. 4 on a larger scale.

'Fig. 6 shows a valve on a still larger scale.

' Fig. 7 is a" longitudinal section of a portion of the forepart of thehull, carrying a bow rudder forming part of my invention and illustratedtogether with its actuating members.

the same form as the forepart but is provided with a keel 24 projectingrearwardly toward the rudder 26.

The forepart 22 is provided with a rudder 28 carried by a'shaft 30penetrating through the bottom 29 of the tanks 34 and 36 communicatingdirectly with the sea through relatively large openings 38. Extendingfrom the upper limiting wall 40 of the tanks are conduits 42 provided'with top valves 44. When the valves 44 are opened, air-present in thebottom tanks will rapidly escape therefrom and water will enter thetanks through the openings 38. j The valves may be constructed forautomatic con-' i trol and 'for this purpose be pivoted about a shaft 46(Fig. 6) and provided with an arm 48 carrying a weight 50. Such valveswill operate automatically, for example upona sheer -or yaw of .theship, the valve being raised due to the listing of the ship, thusopening a communication withthe ambientatmosphere so as'to cause thetank controlled by said valve to be filled by water replacing the airpermitted to escape. The actuation of the valves thus results from thelisting movement of the ship but-it is also dependenton the centrifugalforce.

'The tanks 34 and 36 may also be interconnected'by a conduit 52. Saidconduit includes a compressor 54 and valves 56. By means of thecompressor 54 air may be introduced into either tank or into both tanksat the same time while displacing a corresponding quantity of water outof the ship. It is alsopossible to pass air through the 'conduit.52 fromone tank tothe other, the quantity of water being increased in theformer and reduced in the lattertank.

When a wave initiates a rolling movement of the ship about itslongitudinal axis in onedirection, the front rudder 28 causes animmediate change of course in the same direction, which results in aneutralization in anearly stage of the rolling movement. 'When at thenext moment'the waves tend to roll the ship in the opposite direction,the front rudder 28 reacts and initiates a change of course directlyopposite tothe former, thebalance of the deviations from the principalcourse thus being .restored. The ship will only perform a very slightchange of course to meet every wave, such changes always inter-- ruptingand'neutralizing the rolling movement, so that the change of the centerof gravity of the ship in the lateral direction caused by passengerswalking from one railing of the ship to the other.

Assuming a ship being formed as a cylinder or spool floating on thewater, all reactions of the ship to the attacks of the waves will bedirected through the aiXs of rotation of the spool. With a metacentricheight of 0 such ship would consequently remain entirely ,uninfluencedby the attackof the waves OIlzltSSldfiS. The ship would then moveentirely undisturbed by the surrounding sea as far as angular movementsabout the longitudinal axis are=concerned.

Thehull formed according to Figs. 13 by circular arcs approaches theproperties of'the cylinder in such respect, since the dynamicjforcesproduced-by the surrounding sea constitute the normal to the circularlyshaped sides of the ship and may be caused to attack near the metacenterof the ship. The less the-force resultantproducediby'the sea deviatesfrom the metacenter, orthe closer itcoincidfis .displacernenttof.20,00tons. .The abscissa in;Fig. 10 1mdicates the listing angle ot the'ship,.and;the;ord inate latter becomes negligible, if perceptible atall to thepassengers,

The capability of the ship to perform the continuous deviations from themain course in response to each wave is largely 'due to the particularform of the ships 'hull described above. The following table indicatesthe speeds and wave periods of sea waves having different lengths:

The ship must thus-be capable of reacting within-the wave-periods to theimpulses imparted" thereto by the ruddera28.

.According to traditional concepts, thehull ofa. ship of thetypeillustratedin Figs. 1+3 will perform the minimum of disturbing. rollingwhen loaded as deeply as with a displacement of 2000 tons, for example,to have ametacentric height between 0314 and 0.3:meterr. :If the'loadis-reduced, the ship becomes more cranky. The capacity of the tanks 34and 36 is selected so as to give to the ship when the tanks aresubstantially clear of water, a:metacentric height approaching 0.Said-height'may be advantageously negative, in which latter case theship is brought intoan unstable position of equilibriumand, when lyingstill, is imparted a slightlist toward one or the other side. The shipwill then have two stability centers near each other, whichresult isobtained by a negative metacentric height of a few centimeters. In thiswaythe ship will, within a listing rangeof aplurality of degrees, attaina position. of equilibrium .cohtrellableby the bottom tanksand capableof -being adjusted :from normal; stability to: a; floating indefiniteposition adapted to :be influenced by exceedingly small -forces, such;as a moment ofa few: hundreds ofkilograms in'a ship having adisplacement 0f 2000 tons. .The, position of-equilibrium is then :also,influenced; by small :forces, for. instanceby a indicates: the erecting;lever: GZ incentimeters. Thecnrve 58 :relates to a: hull constructedaccording o 1 my inventiontwithlametacentric height equalling 30centimeters,

- whilethecurve .60 relates to a hull withtazmetacentric and having ametacentric. height of Owith respect to static stability ranks equalwith the conventional hull having a metacentric height of14.4,centimeters. The type of hull usediaccording. to my. invention thuspermits .of a lower tmetacentric "height than .does the.conventional.hull -,in

order to possess the samestability.

Fig.;l1 relatesto the :dynamic .stability whiehfifor'the hullaembodyingmy invention and having ametacentric height equalling 0 is: indicated bythe curve-6,0,- and which .for the statically.comparableconventionalrhull withua metacentric-heightof 14.4 centimetersisindicateduby the curve*62. .In. this case too, the abscissav indicatesthe listing angle (p, while the ordinate indicates the=so,.-cal1eddy-namiclever e. It .will appear from Fig. 11that;the

quantity 10f .work. accumulated. by a listing andtequalling e timesflthedisplacementis smaller in.thezhull$made. according to my invention thanin the conventionallhull.

This involves a considerablysmaller. force. being required according tomy invention to restore. theship toeantupright position upon initiationof a'listingmovementthan is required in a ship ofconventionalconstruction. Said figure-shows further that the difierence between thehulls is particularly evident for listing. angles below .5. .The valueof the -work.required forcounteracting a rolling -movement of the shipis understood-to be for the ship represented by the curve tov be onlyafraction-otithe work required'for the ship represented:by.the curvea62,as farassmall listingangles are concerned.

-With greater listing'angles, suchas anglesrfiacbing =01 even-surpassing30, when the :risk-of: capsizing istof rconverginguerosssseetional shapeofthe hull will thusbe understood;to'idesignate;a hullcreating stabilitycurves I of the character illustrated in said figures.

It will be understood from the above explanation that the form of hullused according to my invention is highly suited to eliminate rolling ofthe ship by means of the front rudder 28. The force required tocounteract the listing initiated by the wave will be small and may,therefore, be produced by the rudder 28 without difiiculty.Paradoxically as it may seem, the ship is made cranky in order to attaina stable motion uninfluenced by the waves. The metacentric height mayeven be negative, in which case the center of gravity is located abovethe metacenter. The ship moves forwardly in the same way as a bicycle,where the front wheel corresponds to the rudder 28 and Where thesupporting points are located below the center of gravity. With alateral load, such as a gust of Wind, acting on the cyclist and tendingto incline the bicycle to the right, the cyclist automatically turns thefront wheel somewhat in the same direction, and the balance isimmediately restored.

To attain the capability of instantaneous reaction to the rudder 28required to control the rolling of the ship by small lateral changes ofcourse, the above described shape of the forepart of the ship is also ofimportance. The forepart thus facilitates rapid changes of course of theship to maintain its balance. In this respect the forepart shapedaccording to my invention substantially difiers from the conventionalstem or bow portion with a vertical profile penetrating deeply into thewater.

Another factor having an influence on the motion of the ship through theWaves is the oscillatory period of the ship in a rolling motion. Asalready stated the oscillatory period increases with a decreasingmetacentric height of the ship. With a constant metacentric height theoscillatory period is longer at smaller listing angles than at largerones. In this respect also the hull constructed according to myinvention is superior to the conventional hull, as will be understoodfrom Fig. 12, where the abscissa indicates the listing angle (p and theordinate the oscillatory period T calculated in seconds. Curve 66relates to an arc-shaped hull having a metacentric height of 0, whilecurve 68 relates to the conventional hull having a metacentric heightequalling 14.4 centimeters and possessing an equal static stability.According to the curve 66 the oscillatory period decreases strikinglywith an increasing listing angle. Thus the hull constructed according tomy invention has no tendency of getting into resonance with theoscillatory period of the waves, which is presumed to be constant or atany rate to be altered very slowly.

Rubber suspension is Well known to be an exceedingly effective means forthe damping of vibrations such, for example, as are imparted to adjacentparts by a high speed engine. This damping quality of the rubber resultsfrom its modulus of elasticity not remaining unchanged by theoscillatory amplitude but rapidly being changed in response thereto. Therubber thus does not lend itself to synchronous oscillations, and a shipaccording to my invention shows the same damping quality with regard toan actuation by the surrounding sea.

As it is consistent with common practice to have the rudder of a shipcontrolled by a gyroscope or gyrocompass over a servomotor in order tokeep the course of the ship in the direction of the voyage, the timecontrol of the gyroscope reacting to the speed of angular movementsperformed by the rudder 26 is adjusted, according to the invention, soas to operate in a slower and preferably many times slower pace betweentwo angular end positions of the rudder-than does the gyro-controlledbow rudder 28 located under the forepart of the ship. These measures arenecessary to prevent the rapid immediate actuation created by therolling movements of the ship from being intermixed and getting intophase with the movements of the main rudder of the after-part.

The bow rudder is thus a rapidly operating balancing member of the ship,which as a rule produces small forces to create very small angulardeviations to both sides, whereas the main rudder is intended to steerthe ship in the desired course.

The gyro-control of the rudder 28 may be put out of operation and saidrudder instead be operated manually. The ship may thus be prepared, forinstance, for a powerful sheer to port by a manually initiatedpreparatory turn to starboard by the rudder 28, which turn to starboardcauses overbalancing to port, before the more or less sharp sheer toport is made by both rudders 26 and 28. In this way, a lurch that wouldbe unpleasant to the passengers is avoided. During the preparatory turnto starboard, the port tank or tanks may be filled with water, whereaswater is discharged from the starboard tank or tanks.

As will be understood from the preceding explanation, the water tanks 34and 36 do not have for their object directly to counteract the rollingof the ship, their main object being to raise and to lower the center ofgravity of the ship in order to impart to the ship a maximum of softmotion in response to the nature of the waves. However, the tanks may beused to counterbalance a onesided load, for instance due to the wind orthe passengers gathering on one side of the ship. In this case thesuitable position of the center cf gravity is attained by acorresponding variation of the contents of the tanks underconsideration.

The rudder 28 may be actuated by means other than gyroscopes, forinstance by a pendulum, responding to oblique positions of the ship. Thetanks may be located at various places in or on the ship, thus includinglocation on deck. The change of the metacentric height may also becaused by a weight transfer within the ship.

While several more or less specific embodiments of the invention havebeen shown, it is to be understood that this is for purpose ofillustration only, and the invention is not to be limited thereby, butits scope is to be determined by the appended claim.

What I claim is:

A method of controlling and counteracting the rolling movements due towave action of a ship having a rollsensitive hull substantially V-shapedin cross section and having a keel line arcuate from a pointsubstantially amidships to the bow thereof and responsive to a rudderdisposed adjacent the bow for stabilizing purposes, said methodcomprising automatically creating and applying a lateral force to thehull adjacent the bow in response to and proportional to a rollingmovement of the portion of the hull above the longitudinal axis of rollin one direction, said force being applied transversely to the hull andsubstantially in alignment with the roll axis, said force tending tomove the bow laterally in the direction of said rolling movement,whereby to decrease the rolling of the ship due to wave action.

References Cited in the file of this patent UNITED STATES PATENTS 31,845Winans Mar. 26, 1861 271,213 Bliven Ian. 30, 1883 398,900 Martin Mar. 5,1889 1,529,036 Richey Mar. 10, 1925 1,578,395 Chapin Mar. 30, 19261,780,767 Scott-Paine Nov. 4, 1930 2,202,162 Minorsky May 28, 19402,253,246 Norton et al Aug. 19, 1941 FOREIGN PATENTS 521,734 GreatBritain May 29, 1940 529,474 Germany July 14, 1941

